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Contraindications

The following conditions can affect the accuracy of blood glucose monitoring and it may be necessary to obtain a venous sample for more accurate results (DH 2005).

Peripheral circulatory failure and severe dehydration, for example diabetic ketoacidosis, hyperosmolor nonketotic coma, shock, hypotension. These conditions cause peripheral shutdown, which can cause artificially low capillary readings.

Haematocrit values above 55% may lead to inaccurate levels if the blood glucose level is more than 11 mmol/L.

Intravenous infusion of ascorbic acid.

Preeclampsia.

Some renal dialysis treatments.

Hyperlipidaemia: cholesterol levels above 13 mmol/L may lead to artificially raised capillary blood glucose readings.

Principles of care

Although capillary blood glucose monitoring is an essential part of diabetic management, it can have severe consequences if not done correctly (Wallymahmed 2007). The Department of Health issued a hazard warning in 1987 and a safety notice in 1996 highlighting the need for formal training and strict quality control (DH 1996).

Blood glucose monitoring needs to be performed regularly enough for patterns to be established on which treatment changes can be based (Walker 2004). ‘Regularly’ will vary in different circumstances and any unusual situation, for example illness, change of daily routine, hospitalization, will affect diabetes control and therefore require more frequent testing (Walker 2004). Generally people with type 1 diabetes will need to test blood glucose several times a day or more depending on treatment while those with type 2 will require less testing due to a lower risk of such great fluctuations in blood glucose levels (Goldie 2008). The following list provides guidance on frequency and timing of blood glucose monitoring depending on the type of diabetes and its treatment.

Type 1 diabetes: four or more times daily; more often in unusual circumstances, for example impaired hypoglycaemia awareness, illness, terminal care.

Type 2 diabetes (intensive insulin treatment): as type 1 diabetes.

Type 2 diabetes (conventional insulin): once per day on oncedaily insulin; twice per day on twicedaily insulin.

Type 2 diabetes (insulin and oral treatment): one test a day if on daily insulin or more if control fluctuates.

Type 2 diabetes (diet and exercise; metformin +/− glitazone, glitazone +/− metformin): routine testing not required as low risk of hypoglycaemia.

Type 2 diabetes (sulphonylurea alone or in combination with other oral hypoglycaemic agents): test at least three times a week to detect any unknown hypoglycaemia.

(Owens et al. 2004)

In all the above types of diabetes more regular testing will be required in certain circumstances, for example illness, steroid treatment, changes in diet, exercise and routine (Owens et al. 2004).

For all patients (irrespective of previous diabetic diagnosis) receiving nutritional support, that is enteral or parenteral feeding, blood glucose levels should be checked once or twice daily (or more if needed) until stable and then weekly (NICE 2008).

Methods of blood glucose testing

Blood glucose testing involves obtaining a drop of capillary blood and putting it on a testing strip that is read by a blood glucose meter (Goldie 2008). Most meters offer the option of using blood from the finger tips, palm of the hand, upper arm, forearm, calf or thigh (Dale 2006). The most commonly used site is the finger tip as the blood from this area responds rapidly to changes in blood glucose level, as does the blood from the palm of the hand, and therefore delivers the most accurate results (Dale 2006, Goldie 2008). However, the finger tips contain nerve endings which can become sore and less sensitive with frequent testing. The outer parts of the finger are less painful to prick and the thumb and forefinger should be used sparingly due to their continual use in apposition (Goldie 2008). It is important to rotate areas used for blood glucose testing to avoid infection